Active Illumination Polarization Imaging in Turbid Water

This paper presents a systematic study of active polarization imaging in turbid water, focusing on the comparison between circular and linear polarization and the independent separation of forward and backward scattering contributions. Underwater imaging experiments with turbidity levels ranging from 0 to 30 NTU demonstrated that the circular polarization scheme has comprehensive imaging performance significantly superior to the linear polarization scheme, such as more uniform background, lower residual speckle, and higher structural fidelity, because circularly polarized light has the physical advantage of slower depolarization in multiple scattering, enabling it to maintain a high polarization contrast between target signals and background noise. The independent contributions of forward scattering and backward scattering are derived by blackbody substitution difference method (BSDM). Grayscale histogram analysis results reveal that the dominant factor limiting imaging quality in high-turbidity water is the convolution distortion caused by forward scattering, rather than backward scattering, and the convolution distortion cannot be eliminated through simple polarization difference. By experimentally comparing circular and linear polarization schemes and applying BSDM to separate forward and backward scattering, this work confirms the superiority of circular polarization scheme and proposes BSDM as a reliable and easily implementable analytical method for turbid water polarization imaging.